1. Field of the Invention
This invention relates to downhole sealing, and to an apparatus and method for use in forming an arrangement to allow creation of a downhole seal. In particular, but not exclusively, the invention relates to the provision of a seal or packer between concentric downhole tubing, such as bore-lining casing and production casing.
2. Description of the Related Art
In the oil and gas exploration and production industry, bores are drilled to access hydrocarbon-bearing rock formations. The drilled bores are lined with steel tubing, known as casing, which is cemented in the bore. Oil and gas are carried from the hydrocarbon-bearing or production formation to the surface through smaller diameter production tubing which is run into the fully-cased bore. Typical production tubing incorporates a number of valves and other devices which are employed, for example, to allow the pressure integrity of the tubing to be tested as it is made up, and to control the flow of fluid through the tubing. Further, to prevent fluid from passing up the annulus between the inner wall of the casing and the outer wall of the production tubing, at least one seal, known as a packer, may be provided between the tubing and the casing. The tubing will normally be axially movable relative to the packer, to accommodate expansion of the tubing due to heating and the like. The packer may be run in separately of the tubing, or in some cases may be run in with the tubing. In any event, the packer is run into the bore in a retracted or non-energised position, and at an appropriate point is energised or xe2x80x9csetxe2x80x9d to fix the packer in position and to form a seal with the casing. A typical packer will include slips which grip the casing wall and an elastomeric sealing element which is radially deformable to provide a sealing contact with the casing wall and which energises the slips. Accordingly, a conventional packer has a significant thickness, thus reducing the available bore area to accommodate the production tubing. Thus, to accommodate production tubing of a predetermined diameter, it is necessary to provide relatively large diameter casing, and thus a relatively large bore, with the associated increase in costs and drilling time. Further, the presence of an elastomeric element in conventional packers limits their usefulness in high temperature applications.
It is among the objectives of embodiments of the present invention to provide a means of sealing production tubing relative to casing which obviates the requirement to provide a conventional packer, by providing a relatively compact or xe2x80x9cslimlinexe2x80x9d sealing arrangement which does not require the provision of slips and elastomeric elements to lock the arrangement in the casing.
According to one aspect of the present invention there is provided a method of providing a downhole seal in a drilled bore between inner tubing and outer tubing, the method comprising: providing an intermediate tubing section defining means for sealingly engaging with the inner tubing; and plastically deforming the intermediate tubing section downhole to form an annular extension, said extension creating a sealing contact with the outer tubing.
The invention also relates to a downhole seal as formed by this method.
The invention thus permits the formation of a seal between inner and outer tubing without requiring the provision of a conventional packer or the like externally of the inner tubing. In the preferred embodiment, the intermediate tubing section is of metal and the invention may thus be utilized to create a metal-to-metal seal between the intermediate tubing section and the outer tubing. The sealing means between the intermediate tubing section and the inner tubing may be of any appropriate form, including providing the intermediate tubing section with a polished bore portion and providing the inner tubing with a corresponding outer wall portion defining appropriate sealing bands of elastomer, which permits a degree of relative axial movement therebetween. In other embodiments, the sealing means may be in the form of a fixed location seal. In other aspects of the invention the intermediate tubing may be omitted, that is the inner tubing itself may be deformed to engage the outer tubing.
The outer tubing may be elastically deformed and thus grip the extension, most preferably the deformation resulting from contact with the extension as it is formed. In certain embodiments, the outer tubing may also be subject to plastic deformation. Accordingly, the outer tubing need not be provided with a profile or other arrangement for engagement with the intermediate tubing portion prior to the formation of the coupling.
Preferably, the inner tubing is production tubing, or some other tubing which is run into a drilled bore subsequent to the outer tubing being run into the bore. Preferably also, the outer tubing is bore-lining casing. Accordingly, this embodiment of the invention may be utilized to obviate the need to provide a conventional production packer, as the intermediate tubing section forms a seal with the outer tubing and sealingly receives the inner tubing. This offers numerous advantages, one being that the inner tubing may be of relatively large diameter, there being no requirement to accommodate a conventional packer between the inner and outer tubing; in the preferred embodiments, the intermediate tubing section requires only a thickness of metal at the sealing location with the outer tubing, and does not require the provision of anchoring slips or a mechanism for allowing slips or a resilient element to be energized and maintained in an energized condition. Alternatively, the outer tubing may be of relatively small diameter to accommodate a given diameter of inner tubing, reducing the costs involved in drilling the bore to accommodate the outer tubing.
Preferably, said deformation of the intermediate tubing section is at least partially by compressive yield, most preferably by rolling expansion, that is an expander member is rotated within the tubing section with a face in rolling contact with an internal face of said section to roll the tubing section between the expander member and the tubing section. Such rolling expansion causes compressive plastic deformation of the tubing section and a localised reduction in wall thickness resulting in a subsequent increase in diameter. The expander member may describe the desired inner diameter of the extension, and is preferably urged radially outwardly into contact with the section inner diameter; the expander member may move radially outwardly as the deformation process progresses, progressively reducing the wall thickness of the intermediate tubing section.
Preferably, at the extension, the intermediate tubing section is deformed such that an inner thickness of the tubing section wall is in compression, and an outer thickness of the wall is in tension. This provides a more rigid and robust structure.
At least a degree of deformation of the intermediate section, most preferably a degree of initial deformation, may be achieved by other mechanisms, for example by circumferential yield obtained by pushing or pulling a cone or the like through the intermediate section, or by a combination of compressive and circumferential yield obtained by pushing or pulling a cone provided with inclined rollers or rolling elements.
Preferably, the intermediate tubing section is plastically deformed at a plurality of axially spaced locations to form a plurality of annular extensions.
Preferably, relatively ductile material, typically a ductile metal, is provided between the intermediate tubing section and the outer tubing, and conveniently the material is carried on the outer surface of the intermediate tubing section. Thus, on deformation of the intermediate tubing section the ductile material will tend to flow or deform away from the points of contact between the less ductile material of the intermediate tubing and the outer tubing, creating a relatively large contact area; this will improve the quality of the seal between the sections of tubing. Most preferably, the material is provided in the form of a plurality of axially spaced bands, between areas of the intermediate tubing section which are intended to be subject to greatest deformation. The intermediate tubing section and the outer tubing will typically be formed of steel, while the relatively ductile material may be copper, a lead/tin alloy or another relatively soft metal, or may even be an elastomer.
Preferably, relatively hard material may be provided between the intermediate tubing section and the outer tubing, such that on deformation of the intermediate tubing section the softer material of one or both of the intermediate tubing section and the outer tubing deforms to accommodate the harder material and thus facilitates in securing the coupling against relative axial or rotational movement. Most preferably, the relatively hard material is provided in the form of relatively small individual elements, such as sharps, grit or balls of carbide or some other relatively hard material, although the material may be provided in the form of continuous bands or the like. Most preferably, the relatively hard material is carried in a matrix of relatively ductile material.
Preferably, the method comprises the step of running an expander device into the bore within the intermediate tubing section and energising the expander device to radially deform at least the intermediate tubing section. The expander device is preferably fluid actuated, but may alternatively be mechanically activated. The device may be run into the bore together with the intermediate tubing section or may be run into the bore after the tubing section. Preferably, the device defines a plurality of circumferentially spaced tubing engaging portions, at least one of which is radially extendable, and is rotated to create the annular extension in the tubing section. Most preferably, an initial radial extension of said at least one tubing engaging portion, prior to rotation of the device, creates an initial contact between the intermediate tubing section and the casing which is sufficient to hold the tubing section against rotation.
As noted above, in other aspects of the invention the intermediate tubing section may be omitted, or provided integrally which the inner tubing. For example, the inner tubing may be production tubing and may be deformed to engage surrounding casing. Embodiments of this aspect of the invention may include some or all of the various preferred features of the first-mentioned aspect of the invention, and may be installed using substantially similar apparatus.
Other aspects of the invention relate to locating tubing sections in existing tubing for use in other applications, such as serving an a mounting or support for a downhole device, such as a valve.
According to another aspect of the present invention there is provided apparatus for use in forming a downhole arrangement for permitting sealing between inner tubing and outer tubing utilizing an intermediate tubing section fixed to and in sealing contact with the outer tubing and for sealingly engaging the inner tubing, the apparatus for location within the intermediate tubing section and comprising a body carrying a plurality of circumferentially spaced tubing engaging portions, at least one of the tubing engaging portions being radially extendable to plastically deform the intermediate tubing section, the body being rotatable to form an annular extension in the intermediate tubing section for sealing engagement with the outer tubing.
The invention also relates to the use of such an apparatus to form said downhole arrangement.
Preferably, the apparatus comprises at least three tubing engaging portions.
Preferably, the tubing engaging portions define rolling surfaces, such that following radial extension of said at least one tubing engaging portions the body may be rotated, with the tubing engaging portions in contact with the intermediate tubing section, to create the intermediate tubing section extension. In other embodiments the extension may be created in a step-wise fashion.
Most preferably, the tubing engaging portions are in the form of a radially movable rollers. The rollers may have tapered ends for cooperating with inclined supports. At least one of the supports may be axially movable, such movement inducing radial movement of the rollers. Preferably also, each roller defines a circumferential rib, to provide a small area, high pressure contact surface.
Preferably, said at least one tubing engaging portion is fluid actuated. Most preferably, the tubing engaging portion is coupled to a piston; by providing a relatively large piston area with respect to the area of the portion which comes into contact with the tubing it is possible to produce high pressure forces on the tubing, allowing deformation of relatively thick and less ductile materials, such as the thicknesses and grades of steel conventionally used in downhole tubing and casing. Most preferably, a support for the tubing engaging portion is coupled to a piston, preferably via a bearing or other means which permits relative rotational movement therebetween.
The apparatus may be provided in conjunction with a downhole motor, or the apparatus may be rotated from surface.
The apparatus may further include other tubing expansion arrangements, particularly for achieving initial deformation of the tubing, such as cones, which cones may include inclined rollers.
The apparatus may be provided in combination with an intermediate tubing section.
In other aspects of the invention, the apparatus may be utilized to locate a tubing section for use in other applications, for example as a mounting for a valve or other device, in a bore.